Tuberculosis remains one of the most significant global causes of morbidity and mortality from infectious disease, and an effective vaccine for controlling Mycobacterium tuberculosis (Mtb) has yet to be found. Well established correlates of vaccine induced protection against Mtb have not been established, and it remains to be shown that the immune system is capable of achieving high levels of bactericidal immunity against this organism. Along with our colleagues in the tuberculosis research group at Einstein, we have recently produced and characterized a genetically engineered form of the rapidly growing nonpathogenic M. smegmatis that can induce an extraordinary and unprecedented level of protective immunity in mice against Mtb. Initial studies show that mice immunized with this M. smegmatis strain, which we designate IKE+, can respond to challenges by virulent Mtb with rapid induction of a high level of bactericidal immunity. This is associated with unprecendented reductions in tissue bacterial levels, and in some cases even complete sterilization of tissues with apparent cure of tuberculosis. Preliminary adoptive transfer studies show that this immunity is dependent on a population of memory CD4+ T cells, which are able to transfer a significant level of the bactericidal response to naove animals. Furthermore, the induction of this population of CD4+ T cells appears to be dependent on the presence of B cells in the immunizing environment. These findings define a new experimental system in which to seek correlates of bactericidal immunity against M. tuberculosis, which we will use to identify the characteristics of the specific T cell populations that are capable of inducing the remarkable anti-mycobacterial responses. In this two year project, we propose to identify the phenotype and antigen specificities of the relevant T cell populations, and extensively characterize their functional activities with respect to production of key cytokines and other effector molecules. These studies are likely to reveal previously unexplored mechanisms by which the immune system can control and eliminate Mtb, and have potentially major implications for development of tuberculosis vaccines. PUBLIC HEALTH RELEVANCE: Tuberculosis remains one of the most important global causes of morbidity and mortality from infectious disease. This proposal is an integral component of a program that aims to understand in greater detail the mechanisms by which the immune system can be made to recognize and kill Mycobacterium tuberculosis following specific immunization with novel experimental vaccines. The goal of the research is to establish principles that will enable the design and construction of better vaccines for the prevention of tuberculosis.